Concept albums are nothing new, but the story behind the latest seven-inch from the band Tennis feels pretty fresh. The summery, lo-fuzz songs on the “Marathon” EP, which was released this week on Underwater Peoples, are based on the sailing trip taken by the husband-and-wife duo Patrick Riley and Alaina Moore in 2009 — an eight-month journey along the East Coast that took them from “Bimini Bay” in the Bahamas through “Marathon” Florida, “South Carolina” and up to “Baltimore” on their 30-foot “Cape Dory.” Not bad for two kids from Denver who’d never sailed before.

With $1,600 and a knowledge of the seas that came entirely from “The Annapolis Book of Seamanship” and DVDs, the couple set off for a year of adventure (sharks, reefs, storms, navigating by hand-bearing compass) that would fulfill Riley’s childhood dream. What they couldn’t predict was that being cut off from the United States music scene — limited power on the boat meant that they could only listen to a handful of songs every day — meant they’d come to discover their own sound.

“There were no instruments on the boat — we had to reacquire all the musical equipment we sold to take the trip in the first place,” said Moore, who was home on her day off from her retail job. “One day we were in a bar in the Florida Keys and ‘Baby It’s You’ by the Shirelles came on. We’d never heard it before, but we loved the wall-of-sound thing, and decided right then that we’d try to create that when we got back.”

They started writing the songs, which have a pleasantly angular take on the girl-group sound, at home this past January as a way to process the trip. Their sailing blog, White Satin Gloves — which they quickly typed up while they plugged in their power strip at bars — couldn’t convey their incredible journey. “It was a huge letdown going back to regular life and not being able to express things, like how a shark was feeding next to us while we were eating oatmeal,” said Moore. “Every song reminds us of time, place, people and experiences,” from the beauty of the Carolina waterways to their depressing glimpses of Florida, where “everyone either works in a bar or drinks all day.”

The young couple saved for six years to be able to buy the boat and take the time off. Riley, who just left his job in facilities and installation at Denver’s Museum of Contemporary Art, said the trick was to cut back on bars and restaurants, as well as concerts: “We’re really miserly,” he said with pride. This past year, they’ve been able to save enough to head off again in the fall, but since their music went (indie) viral, they wonder if they’ll be able to tour as offers come in — and there’s still that full-length to record.

But Riley said they need go to go away in order to move ahead. “We need another writing sabbatical,” as he called it. “A lot of our creativity and freshness of perspective came from not being engulfed in music.” However, don’t expect a Sufjan Stevens-like musical catalog of the oceans. “The next trip, we’ll go sailing and be able to reflect back on our life in the States,” said Riley. “It’s a perspective thing.” Listening to the songs on “Marathon,” it’s an idea that holds water.